This invention relates to a method of manufacturing a colour picture tube and more particularly to a method of exposing the photosensitive substances coated on the panel of the tube for preparing a fluorescent screen including a plurality of continuous stripe shaped three colour phosphors. The exposure light is projected through a plurality of parallel stripe shaped perforations of a colour selecting member or electrode (hereinafter called a colour selecting member), the perforations extending in one direction of deflection of the electron beam, and each one of said stripe shaped perforations being divided into a plurality of slit shaped sections by bridges extending in a direction perpendicular to the longitudinal direction of the perforation.
As is well known in the art the fluorescent screen of a colour picture tube is prepared by regularly coating photosensitive substances on the inner surface of the face plate and then exposing the photosensitive substances to light by using an exposure device 1 as diagrammatically shown in FIG. 1. The exposure device shown in FIG. 1 comprises a source of point light 2 and a correcting lens 3 for causing the light emanated from the source 2 to approximate the actual locus of the electron beam of a completed colour picture tube. A colour selecting member 4, typically a perforated shadow mask, and a panel 5 supporting the colour selecting member 4 are mounted on the exposure device 1. Photosensitive substances are coated on the inner surface of the panel 5 and exposed to the light emanated from the source of point light 2 and transmitting through the colour selecting member 4 and correcting lens 3 to form a fluorescent screen of a predetermined pattern.
With a widespread use of colour television receivers in recent years, various types of colour picture tubes have been developed. In one type, a colour selecting member provided with a plurality of parallel stripe shaped perforations is used. With this type of the colour selecting member, because it is not necessary to adjust the electron gun assembly in the longitudinal direction of the stripe shaped perforations it is possible to obtain reproduced pictures of higher colour purity with more simple electronic circuit than the well known shadow mask type colour picture tube.
However, since the stripe shaped perforations are formed to cover substantially the full width of the colour selecting member its mechanical strength is small so that it tends to vibrate due to mechanical shocks or large volume sound from a speaker incorporated in a colour television receiver during the use thereof, thereby causing undesirable colour shading. To obviate this difficulty, the stripe shaped perforations are divided into a plurality of slit shaped sections by providing suitably spaced apart bridges extending in a direction perpendicular to the longitudinal direction of the perforations. Such bridges function to reinforce the colour selecting member. However, these bridges intercept the light utilized to expose the photosensitive substances so that resulting stripe shaped three colour phosphors are interrupted at portions corresponding to the bridges.